RED DEER – Spreading manure on forages is an uneven science.
Manure is cheaper than commercial fertilizer if used efficiently and properly, but its nutrient content varies. Relying on animals to do the work of spreading their own manure provides inconsistent results, said Vern Baron of Agriculture Canada and the Western Forage Beef Group based at Lacombe, Alta.
“You have to deal with the impact of animal behaviour,” he said at a recent manure management conference.
There could be more nitrogen found in the soil close to mineral and watering sites because the animals congregated in those spots.
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The feces and urine from a 1,500 pound cow and a calf per acre over 100 days results in about 72 lb. of nitrogen, 27 lb. of phosphorus and 99 lb. of potassium. However, even in well managed pastures it is hard to spread that manure evenly. Most of the excretions end up in about 15 percent of the pasture so it is wise to not apply commercial fertilizer in those spots.
That leads to using the “cowboys’ version of precision agriculture,” said Baron.
Soil probes and mapping pasture zones are needed because no two fields are the same and additional fertilizer may be needed in some spots to balance a paddock.
“In most farming ecosystems we usually have to add some fertilizer nutrients to balance this equation because this whole business of removal has a big impact,” he said.
Plants take different amounts of nutrition from the soil. In the first year of production the grass may not need fertilizer but many old pastures appear to have fewer nutrients available to the plants. The older the pasture, the more the microbial mass grows. These microbes require more soil nutrients so less is available to plants.
It is also feasible to mechanically spread manure on forages but the challenge of even distribution and nutrient content remain, said Shabtai Bittman of Agriculture Canada at Agassiz, B.C.
“It is not easy to use manure as the principal fertilizer source. You have to depend on reliable and predictable response. You have to be able to apply the product uniformly,” he said.
“There is an issue of the balance of nutrients which rarely is appropriate for the crop requirements.”
Manure takes more time to apply than chemical fertilizer and there is the risk of odour and nutrient loss when nitrogen turns to gas and dissipates into the atmosphere.
However, applying manure on grass is a good idea because there is a high nutrient uptake by grasses as long as the material gets under the plant canopy so there is less volatilization. There is a high level of ammonium in manure, an energy source for soil microbes to oxidize and turn into nitrates for the plants.
There is also an opportunity for season-long manure application as opposed to applying it to a grain crop. There is less leaching or runoff compared to manure spread on bare soil.
“Grass is very good at soaking up nitrogen,” Bittman said.
Liquid manure on grasses cannot be easily incorporated into the soil with many of the machines available. Some spreaders can deliver manure uniformly with drop hoses that band slurry directly on the sod surface or floating shoes that slide on the ground. These are called a drag shoe or sleigh foot.
A three year research project at Agassiz looked at responses of grass to broadcast surface and banded dairy slurry.
Agriculture Canada has developed an applicator called the AerWay SSD. It is a low disturbance machine that bands manure over a row of vertical aeration openings. It has a sleigh foot applicator with twice the efficacy of a trailing hose.
Researchers found a sleigh foot or banding helps reduce ammonia loss and odour concerns.
Grass receiving manure from a splash system often yielded less than fertilizer. Many farmers already knew this and were reluctant to use a splash system because of poorer yields.
